The present invention relates generally to integrated circuit packaging and, more particularly, to integrated circuit packages formed on laminated substrates, such as BGA (Ball Grid Array) and PBGA (Plastic Ball Grid Array) packages.
As integrated circuits become more complex, a need has arisen for an integrated circuit package having a greater number of high-density, reliable, external electrical connections. For the integrated circuit package, it is desirable to include one or more conductive layers for signal routing and/or provision of ground and/or power planes. To meet these needs, substrate-based packages such as BGA have been developed.
In addition, to protect the semiconductor dies and bond wires from damage during handling, physical protection means such as a mold cap is formed on the substrate. A mold cap is formed on the substrate by a transfer or injection molding process. To prevent voids, the mold cap usually has chamfered areas at each of the corners of the substrate. These chamfered corners, unfortunately, leave the corners of the substrate exposed. Thus, the solder mask at the substrate corners is susceptible to cracking during handling. Larger size packages (e.g., 29 mm×29 mm and 31 mm×31 mm) are even more susceptible to solder mask cracking.
FIGS. 1 and 2 show a conventional molded BGA device 10. The device 10 includes a substrate 100 having a plurality of conductive traces 102 and vias 104 (only one is shown), a semiconductor die 106 attached to the substrate 100 with a die attach material 108, and a mold cap 110 formed on the substrate 100 to cover and protect the die 106 and bond wires 112 that electrically connect the die 106 to the conductive traces 102 of the substrate 100. The semiconductor package 10 also has external electrical connectors in the form of solder balls 114. Typically, before forming the mold cap 110, a solder mask 116 is formed on the substrate 100 to prevent corrosion and oxidation of the conductive traces 112 of the substrate 100.
As can be seen in FIG. 1, the corners 118 of the mold cap 110 are clipped or chamfered so that the sides 120 of the mold cap 110 do not intersect at right angles. This has been found useful to prevent the intrusion of moisture between the junction of the mold cap 110 and the upper surface of the substrate 100. However, the clipped corners 118 of the mold cap 110 expose the solder mask 116. During handling, the exposed solder mask 116 has a high risk of cracking, which in turn makes the traces 102 susceptible to fracture.
Therefore, it would be desirable to improve the integrated circuit packages to solve the above problem.